Presentation for CAPSiDE Tech Talks about how to write great Nagios plugins in Perl for the Nagios-compatible monitoring solution of your choice

1. Writing plugins for Nagios and Opsview
Jose Luis Martinez
CTO
2014-02-11 Barcelona
architects of the digital society
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2. Nagios
What is Nagios?
Opsview? Icinga? Naemon? Shinken?
architects of the digital society
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3. Opsview
 Configures and runs Nagios for you
 Presents a frendlier and more powerfull user
interface
 Implements Nagios best practices
 Distributed Monitoring
 Datawarehouse
architects of the digital society
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4. Back to Nagios
 Monitoring tool that doesn’t know how to monitor
anything!?!?
• The real monitoring is done by plugins
• Just external programs with a defined interface to communicate with Nagios
• Written in any language
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5. Plugins
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6. Writing your plugins
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7. First rule
 Is it already done?
• www.monitoring-plugins.org
• Plugins project
• www.nagiosplugins.org
• Nagios official plugins
• www.monitoringexchange.org
• User contributed
• exchange.nagios.org
• User contributed
• Google “xxx nagios”
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8. We’ll take a look at
 Nagios::Plugin (Monitoring::Plugin)
 Nagios::Plugin::DieNicely
 Nagios::Plugin::WWW::Mechanize
 Nagios::Plugin::SNMP
 Nagios::Plugin::Differences
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9. Nagios::Plugin
 Lots of common functionality for free!
• When writing a plugin you have to
Handle Arguments
Get and manipulate the data
Calculate state (OK, CRITICAL, …)
architects of the digital society
www.capside.com

10. Nagios::Plugin
 Lots of common functionality for free!
• When writing a GREAT plugin you have to
Handle Arguments
-h –v arguments
-h has to output documentation
Get and manipulate the data
Calculate state (OK, CRITICAL, …)
In a flexible way (in f(x) of arguments)
Output performance data
architects of the digital society
www.capside.com

11. That’s a lot of work
I just wanted to monitor my app!
architects of the digital society
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12. Nagios::Plugin
 Lots of common functionality for free!
• When writing a GREAT plugin you have to
Handle Arguments
-h –v arguments
-h has to output documentation
Get and manipulate the data
Calculate state (OK, CRITICAL, …)
In a flexible way (in f(x) of arguments)
Output performance data
architects of the digital society
www.capside.com

13. 3 Simple Steps
 Setup
 Data collection
 State calculation
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14. Setup
 Just make an instance of N::P
#!/usr/bin/env perl
use Nagios::Plugin;
my $np= Nagios::Plugin->new(
'usage' => 'Usage: %s'
);
$np->getopts;
 You’ve just obtained
• -t option (timeout)
• -v option (verbose)
• --help option
architects of the digital society
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15. Setup (II) Constructor options
 usage ("Usage: %s --foo --bar")
 version <- Version string
 url <- Help and Version
 blurb <- Help description
 license <- Help
 extra <- Help
 plugin <- overrides auto detected name
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16. Setup: GetOpt magic
$np->add_arg(
spec=> 'warning|w=s',
help=> "-w, --warning=RANGE",
required=> 1
);
$np->add_arg(
spec => 'user|u=s',
help => 'Username',
default => 'www-data'
);
$np->getopts;
if($np->opts->user) { … }
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17. Collect data
Now you have to work
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18. State calculation
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19. Ranges
 Most plugins suppose that
• OK<WARNING<CRITICAL
 But… what if…
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20. Ranges
Range definition
Generate alert if x…
10
Is not between 0 and 10
10:
Is not between 10 and infinity
~:10
Is not between –Inf and 10
10:20
Is not between 10 and 20
@10:20
Is between 10 and 20
$code= $np->check_threshold(
check => $value,
warning => $warning_threshold,
critical => $critical_threshold
);
$np->nagios_exit( $code, "Thresholdcheckfailed" ) if ($code!= OK);
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21. Output status
 $np->nagios_exit(CRITICAL, “Too many
connections”);
 $np->nagios_exit(OK, “Everything went fine”);
 $np->nagios_exit(WARNING, “Too few
connections”);
 $np->nagios_exit(UNKNOWN, “Bad options”);
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22. Performance Data
$np->add_perfdata(
label
=> "size",
value
=> $value,
uom
=> "kB",
warning => $warning,
critical => $critical
);
UOM Unit of measurement
Is for
No unit specified
Assume a number of things
s,ms,us
econds, miliseconds, nanoseconds
%
Percentage
B,KB,MB,TB
Bytes
c
A continuous counter
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23. Success!
Enjoy your shiny new plugin
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24. Nagios::Plugin::DieNicely
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25. Nagios::Plugin::DieNicely
 Software fails, and sometimes you don’t control it
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26. Nagios::Plugin::DieNicely
 What happened?
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27. Nagios::Plugin::DieNicely
 What happened?
• Output went to STDERR
• Nagios doesn’t care
• Exit code follows Perls rules
• Nagios understands 0-3
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28. Nagios::Plugin::DieNicely
 use Nagios::Plugin::DieNicely
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29. Nagios::Plugin::WWW::Mechanize
Nagios::Plugin
+
WWW::Mechanize
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30. Nagios::Plugin::WWW::Mechanize
Nagios::Plugin
+
WWW::Mechanize
You where going to do it anyway!
architects of the digital society
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31. Nagios::Plugin::WWW::Mechanize
 Again... Just create an instance. Use it as a
Nagios::Plugin object
 Automatically tracks response time for you
 $np->mech
 $np->content
 $np->get, $np->submit_form
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32. Nagios::Plugin::WWW::Mechanize
A couple of tricks
• Gzipped content
my $np = Nagios::Plugin::WWW::Mechanize->new(
'mech' => WWW::Mechanize::GZip->new(autocheck => 0)
);
• Proxy
my $proxy = $np->opts->proxy;
if (defined $proxy){
$np->mech->proxy(['http', 'https'], $proxy);
}
architects of the digital society
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33. Nagios::Plugin::SNMP
Nagios::Plugin
+
Net::SNMP
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34. Nagios::Plugin::SNMP
Again... Just create an instance. Use it as a
Nagios::Plugin object
Sets up a lot of arguments
Does delta between values of counters
architects of the digital society
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35. Any Questions?
Thanks to:
The Monitoring::Plugin module maintainers
Icanhazcheezburger for the cats
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